Process for the manufacturing of a planographic printing plate capable of being processed into a planographic printing form requiring no wetting

ABSTRACT

In a process for the manufacture of a planographic printing plate which requires no wetting a roughened metallic support is provided with a dispersed layer of polytetrafluoroethylene containing a reducing agent and then treated with a solution containing a noble metal salt, thus forming nuclei of noble metal salt. The layer is then treated with a nickel-plating solution until a continuous nickel layer has been deposited and the deposited nickel layer is then reinforced by electroplating and deactivated by heating to 90* to 100*C, whereupon the dispersed polytetrafluoroethylene layer is sintered at temperatures between 380* and 400*C.

ilnited States Patent [191 Brandt et a1.

Hoechst Aktiengesellschaft, Germany Filed: Sept. 10, 1973 Appl. N0.: 395,550

Assignee:

Foreign Application Priority Data Sept. 11, 1972 Germany 2244486 US. Cl. 427/375; 427/379; 427/380; 427/388; 427/430 Int. Cl. B44D 1/14 Field of Search 117/47 A, 49, 50, 71 M, 117/132 CF, 130 E, 62.1

[451 Sept. 9, 1975 [56] References Cited UNITED STATES PATENTS 3,011,920 12/1961 Shipley, Jr. 117/50 3,399,268 8/1968 Schneble, Jr. et a1... 117/130 E 3,772,078 11/1973 Polichette et al. 1 17/130 E Primary ExaminerCameron K. Weiffenbach Attorney, Agent, or Firm-James E. Bryan 5 7 ABSTRACT In a process for the manufacture of a planographic printing plate which requires no wetting a roughened metallic support is provided with a dispersed layer of polytetrafluoroethylene containing a reducing agent and then treated with a solution containing a noble metal salt, thus forming nuclei of noble metal salt. The layer is then treated with a nickel-plating solution until a continuous nickel layer has been deposited and the deposited nickel layer is then reinforced by electroplating and deactivated by heating to 90 to 100C, whereupon the dispersed polytetrafluoroethylene layer is sintered at temperatures between 380 and 400C.

6 Claims, N0 Drawings PROCESS FOR THE MANUFACTURING OF A PLANQGRAPHTC PRINTING PLATE CABLE OF BEING PROCESSED INTO A PLANOG a .HHC PRINTTNG FORM REQUIRING NO WETTING The present invention relates to a planographic printing plate capable of being converted into a planographic printing form from which printing can be done without having to wet the non-printing areas with water or aqueous solutions.

As is well known, the planographic printing process in its conventional form is based on the discovery that printing forms whose printing areas and non-printing areas are in one and the same plane, may be used for printing when their printing areas are oleophilic and their non-printing areas are hydrophilic, when fatty printing inks are used and when the printing forms are wiped over in a suitable manner with water or with aqueous solutions between ink applications. The constant wetting is the cause of certain disadvantages of the printing process, such as a high consumption of printing ink, wetting of the printed paper, and complicated printing machines. Therefore, efforts have been made to eliminate the use of dampening solutions, and appropriate printing plates already have been developed. They are based on the principle that the nonprinting areas do not consist of hydrophilic material, as hitherto, but of a material which accepts neither water nor greasy printing ink, i.e. which is neither hydrophilic nor oleophilic, and which is sometimes called abhesive. In most cases, this material consists of silicone gum(e.g. U.S. Pat.No. 3,511,178), and in others ofpolymerized multi-fluorinated ethylene (e.g. French Pat. No. 1,465,951).

In some of the known printing forms with abhesive nonimage areas, these areas are the only ones present on the printing form which are made up of abhesive material, because during the preparation of the printing form the adhesive non-image areas have either been applied to the support in a distribution corresponding to the background areas of the image, or the image areas have been imagewise removed from the abhesive layer disposed on the support. The application or the removal of abhesive materials is a relatively complicated process, however, so that many manufacturers of printing forms would prefer to use a printing plate which requires neither the application nor the removal of abhesive material during its conversion into a printing form.

A printing plate of this type is described, e.g., in German Offenlegungsschrift No. 1,571,890 (see FIG. 3 and relevant text). The plate consists of a superficially etched metal support, an abhesive layer thereon, and a Lhin metal foil laminated to the abhesive layer. when the printing plate is processed into a printing form, the printing areas are formed by the metal foil, eg in a manner known per se, with the aid of a light-sensitive, etch-resistant copying layer (photo-resist). Among others, this known printing plate has the disadvantage that the metal layer forming the printing image consists of a self-supporting metal foil, which means that it s rela tively thick. This has not only the drawback that the costs are unnecessarily high, but is also responsible for the fact that the etching process, by which the background areas of the image are removed, takes a relatively long time and that a considerable portion of the details of the image to be printed get lost.

It is the object of the present invention to provide a planographic printing plate which is capable of being processed into a planographic printing form requiring no wetting during operation, in which the image areas are produced in a relatively simple manner and are capable of reproducing an image of an original with a high degree of accuracy. Further, it is the object of the present invention to provide a process for the manufacture of such a printing plate.

The first object is achieved by starting from the abovedescribed known printing plate containing a layer which repels both water and greasy printing ink, in which the layer is supported on a metallic support and is covered by a thin metal coating, but in the planographic printing form according to the invention the layer is sintered polytetrafluoroethylene and the metal coating is a nickel layer which has been deposited thereon by reduction from a nickel bath and then reinforced.

The process for the manufacture of the planographic printing plate according to the invention is based on the known process in which the roughened surface of a metallic support is provided with a layer which repels water as well as greasy ink and the layer is then covered with a thin metal coating. In the process of the invention, the layer applied to the roughened surface of the support is an at least 30 per-cent by weight dispersion of polytetrafluoroethylene containing a reducing activator. It is applied in a quantity such that, after being sintered, the applied dispersion layer completely covers the rough surface. The dispersion layer is dried at temperatures up to I 10C, and the dried layer is then heated at to 220C. The cooled dispersion layer is then treated with a sensitizing solution containing a noble metal salt, thus forming nuclei of the noble metal salt, and the layer is then treated with a nickel-plating solution containing nickel ions and a reducing agent at least until a continuous nickel layer has been deposited.

The deposited nickel layer is then reinforced and killed (deactivated). The polytetrafluoroethylene layer is finally sintered at temperatures between 380 and 400C.

The printing plate according to the invention includes a metallic support. Since a layer of polytetrafluoroethylene is disposed on the support and, at the present state of the art, a continuous layer of polytetrafluoroethylene can be produced only by sintering, the metal foil must be capable of withstanding the sinterin g temperatures. Therefore, the metal support is most advantageously of steel, although other metal foils, such as aluminum foils, also may be used. Advantageously,

the surface of the supporting foil carrying the polytetrafluoroethylene layer is roughened, and the depth of roughening should be at least 3 microns. Depths of roughening of between 3 and 7 microns have proved very suitable.

The thickness of the layer of sintered polytetraflu se, with the aid of noble metal nuclei which are produced on the surface to be coated. A nickel layer produced by electroless plating is normally only 0.2 to 0.3 micron thick and is thus unsuitable for most reproduction purposes. Therefore, the layer is reinforced in the printing plate according to the invention. This may be achieved by repeated electroless plating around noble metal salt nuclei, but is done more advantageously by electroplating.

The printing plate according to the invention may be presensitized by producing, n the nickel layer, a reproduction layer, e.g. a layer containing a diazo compound or an azido compound, or a polymerizable layer. The reproduction layers may be susceptible of etching, e.g. due to a correspondingly high proportion of resin; alternatively, the image may be rendered etchable, e.g. by applying a lacquer after exposure and development of the reproduction layer. It is also possible to sensitize the printing plate by one of the known chromatecolloid layers, but since it is known that these layers cannot be stored, such layers must be applied to the nickel layer shortly before the printing plate is processed into a printing form. Of course, it is also possible to produce the etchable stencil on the nickel layer by other than reprographic processes, e.g. by printing with an etchable mass or by transferring an image stencil which has been produced on another support and is either in itself etch-resistant or can be made etchresistant.

In the inventive process for the manufacture of a planographic printing plate, the roughened surface of a metal foil is covered with a polyethylene dispersion containing a reducing activator. Salts of bivalent tin or hydrazine hydrate were found to be suitable, e. g. tinII- chloride is preferably used in a concentration between 1 and 18 percent by weight, most advantageously be tween 2 and percent by weight. In the case of hydr-azine hydrate, the quantity used is advantageously more than 1 per cent, but less than 5 percent by weight, and preferably between 3 and 4 percent by weight. If less than 1 percent by weight of tin-II-chloride is used, no nickel separation occurs later in the process, whereas at a content of more than 18 percent of tin chloride, the polytetrafluoroethylene layer cracks and comes off in thin laminae when the applied dispersion is dried. The same ocurs when dispersions containing 5 percent or more of hydrazine hydrate are used.

The aqueous dispersions contain at least 30 percent by weight of polytetrafluoroethylene, dispersions containing 40 to 60 percent by weight of polytetrafluoroethylene being preferred.

Polytetrafluoroethylene dispersions contain relatively high proportions of wetting agents, normally 5 percent by weight, calculated on the quantity of polytetrafluoroethylene. In the course of the process, when the polytetrafluoroethylene is sintered, this large quantity of wetting agent becomes particularly annoying in polytetrafluoroethylene layers having a thickness of 3 or more microns. Therefore, polytetrafluoroethylene dispersions are preferred which contain less than 3 percent by weight, more advantageously even less than 1 per cent by weight, of a wetting agent, calculated on the weight of the polytetrafluoroethylene. Further, such dispersions are preferred which contain wetting agents that have a relatively high volatility. The ammonium salt of perfiuorinated caprylic acid, which already evaporates at 150 to 160C, has proved to be a particularly suitable wetting agent.

The polytetrafluoroethylene dispersion is applied in such a quantity that, after the subsequent sintering of the polytetrafluoroethylene dispersion, a layer is formed whose thickness is such that no peaks of the roughened surface of the metallic support protrude from the layer and a completely continuous layer is formed. The aqueous polytetrafluoroethylene dispersion applied in an appropriate thickness is first dried at temperatures between and C. Thereafter, the dried layer is heated to higher temperatures in order to dispel the wetting agent and other volatile components from the layer. For this purpose, temperatures of at least C are preferred, in particular temperatures between 180 and 220C. If the temperature is substantially below 180C, evaporation of the undesirable substances from the dried dispersion layer will normally proceed too slowly. At temperatures above 220C, evaporation would proceed very rapidly, but this involves the risk that the polytetrafluoroethylene layer can be only incompletely nickel-plated because at these temperatures the polytetrafluoroethylene particles begin to sinter. A heating temperature of 200C is preferred and normally a heating time of 10 to 30 minutes is sufficient.

After having been dried, heated, and then cooled, in the manner described, the dispersion layer is treated with a sensitizing solution containing a noble metal salt, most advantageously bathed in the sensitizing solution. A hydrochloric acid solution of palladium chloride is preferred. The solution may contain from 0.005 to 5 percent by weight of palladium chloride, most advantageously about 0.05 percent by weight. Bathing in the sensitizing solution requires from 30 seconds to 3 minutes, in most cases about 1 minute.

Because on the surface of the polytetrafluoroethylene layer the activator meets with the sensitizing agent, nuclei of the noble metal separate. They serve, according to the present process, as catalysts for separating nickel from a bath containing nickel ions and a reducing agent, i.e. the so-called electroless nickel-plating bath. The nickel deposited from the nuclei of the noble metal attaches itself firmly to the polytetrafluoroethylene layer.

When a layer thickness of 0.2 to 0.3 micron has been reached, the electroless nickel deposition gradually ceases. Since the nickel layer of a planographic printing plate must be thicker, i.e normally 1 to 2 microns thick, the nickel layer produced by electroless nickel-plating must be reinforced. It is possible to reactivate the interrupted electroless nickel-plating process by bathing the layer produced by the electroless process in a sensitizing solution. In order to produce a layer thickness of 1 to 2 microns in this manner, however, much more time is necessary than when reinforcing the nickel layer by a galvanic nickel-plating process, so the latter method is preferred.

The reducing agent contained in the electroless nickel-plating bath may be sodium hypophosphite or sodium borohydride. Electroless nickel-plating baths are known and are no part of the present invention. A nickel layer of a thickness of 0.2 to 0.3 micron is normally deposited within 5 to 10 minutes from an electroless nickel-plating bath After reinforcing the nickel layer, the nickel-plated polytetrafluoroethylene layer must be sintered. The

term sintering means heating the material to such a high temperature that the individual polytetrafluoroethylene particles, which were only loosely connected with each other when the polytetrafluoroethylene dispersion was dried, soften and coalesce. Sometimes, this process occurs already at temperatures above 220C, but it is completed at temperatures of 380 to 400C. Besides the improvement of the adhesion, the sintering process causes the surface of the polytetrafluoroethylene layer to become absolutely smooth and abhesive, i.e. repellent towards printing inks, too.

Before the sintering process, however, the reinforced nickel layer must be killed, i.e. rendered inactive. It was found that, after sintering the polytetrafluoroethylene layer, the nickel layer tended to flake off in larger or smaller patches. In some cases, only the electroplated reinforcing layers came off, but in others the reinforcing layers and the electroless deposited layers scaled off. This flaking off may be avoided by allowing a period of time ranging from a few daysto several weeks to elapse between the electro-deposition of the reinforcing nickel layer and the sintering process. It seems that tensions are present in the reinforced nickel layer which are relieved too suddenly by the heating process necessary for sintering, but may be calmed down by a relatively long period of storage. Instead of storing it, the reinforced nickel layer may be killed more rapidly by tempering it at a temperature between 90 and 100C, the tempering process taking between 5 and minutes at 90C and about 2 minutes at 100C.

As already mentioned, the nickel layer may be covered with a negativeor positive-working light-sensitive layer after the sintering process. The light-sensitive layer is applied in known manner.

The nickel layer may be etched away in the nonimage areas by a known electro-chemical process using, e.g., a 72 percent by weight sulfuric acid bath (d 1.62) containing 10g. of glycerol per liter. At room temperature, a current of 6 amperes per square decimeter is allowed to act for about 6 minutes on the nickel layer to be etched, the plate being connected as the anode. The cathode may consist of a lead plate. After the anodic etching processing, the nickel layer is advantageously immersed for 10 to 20 seconds in a 50 percent by weight nitric acid solution and then thoroughly rinsed and dried.

The nickel image formed in the nickel layer after the etching process accepts greasy printing ink, whereas the polytetrafluoroethylene background repels ink.

The printing form thus produced requires no wetting during the printing process. On the contrary, any moistening of the printing form should be avoided.

The printing plate according to the invention is very advantageous for the manufacturer of printing forms, because it can be processed in a relatively simple manner into a printing form from which printing can be done without the use of a dampening solution.

The invention will be further illustrated by reference to the following specific examples:

EXAMPLE 1 A 0.28 mm thick steel plate having one surface roughened to a depth of 3.5 to 4 microns is coated on its roughened surface with a dispersion prepared by mixing the following constituents:

250ml. of a 60 percent by weight polytetrafluoroethylene dispersion containing 0.8 percent by weight of the ammonium salt of perfluorinated caprylic acid as a wetting agent,

50ml. of distilled water,

' 15g. of tin-II-chloride, dissolved in 30ml. of concentrated (36 per cent by weight) hydrochloric acid, and

30ml. of water.

The dispersion contains 40 percent by weight of polytetrafluoroethylene and 4 percent by weight of tin-llchloride; its pH pH-value is 1.

The plate coated with this dispersion is dried for 5 minutes at 90C and then heated for 10 minutes at 200C. Thereafter, the polytetrafluoroethylene layer is 8 microns thick.

The plate is then bathed for 1 minute in an aqueous solution at 25C containing 0.5g. of palladium chloride (PdCl and 1.8g. of 36 percent by weight hydrochloric acid per liter. Subsequently, the plate is rinsed off for 30 seconds with water and then placed for 5 minutes in a bath of C having the following composition:

25.3g. of NiSO. 71-1 0,

24.4g. of sodium hypophosphite,

270g. of d l-lactic acid, and

l6.8g. ,of succinic acid, made up to l,000ml. with distilled water and adjusted to a pH-value of 6.0 by the addition of caustic soda solution. The reducing agent is stabilized by adding a small quantity of telluric acid. The nickel layer deposited from this bath on the polytetrafluoroethylene layer by electroless plating is 0.2 to 0.3 micron thick. By electrodeposition at a temperature of 60C in a nickelplating bath, with the application of l ampere of direct current per square decimeter of the plate, the nickel layer is reinforced to a thickness of 1 micron within 5 minutes.

The plate is rinsed for 30 seconds with water and then tempered for 10 minutes at a temperature of C. Subsequently, the polytetrafluoroethylene layer is sintered for 15 minutes at a temperature of 400C. Thereafter, the polytetrafluoroethylene layer and the nickel layer are inseparably anchored to the steel plate.

The nickel layer is provided with an etchable light- I sensitive layer, exposed through an original, and then developed. After the electrochemical etching process and post-etching in a 50 percent by weight nitric acid solution, a printing plate is obtained whose nickel areas accept greasy ink, whereas its polytetrafluoroethylene areas repel greasy ink without having to be moistened with water.

EXAMPLE 2 v The surface of a steel plate roughened as in Example 1 is coated with a dispersion prepared by mixing the following ingredients:

250ml. of the 60 percent by weight polytetrafluoroethylene dispersion described in Example 1.

25ml. of distilled water,

6g. of hydrazine hydrate, and

7.5g. of sodium hydroxide, dissolved in 87ml. of water. The dispersion contains 40 percent by weight of polytetrafluoroethylene and 1.6 percent by weight of hydrazine hydrate; its pH-value is 10.5.

As in the preceding example, the coated plate is dried at 90 C, then heated to 200C, bathed in a hydrochloric acid solution of PdCI nickel-plated first by the electroless process, then by electrodeposition, tempered at 90C, and finally sintered at temperatures in the range of 300 to 400C. Thereafter, the steel plate,

I the polytetrafluoroethylene layer, and the nickel layer are inseparably united.

By the application of a light-sensitive photoresist layer and etching, as in the preceding example, the nickel layer may be processed into a printing form which may be used for printing without applying a dampening solution.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A process for the manufacture of a planographic printing plate capable of being processed into a planegraphic printing form requiring no wetting which comprises roughening the surface of a metallic support,

coating the surface with an at least about 30 percent by weight dispersion of polytetrafluoroethylene containing a reducing activator capable of reducing a noble metal in a solution of a salt thereof, the quantity of dispersion applied being such that, after being sintered, the dispersion layer completely covers the roughened surface,

drying the dispersion layer at temperatures up to about 1 10C., heating the dried dispersion layer at a temperature between about 180 and 220C,

treating the cooled dispersion layer with a sensitizing solution containing a noble metal salt, thus forming nuclei of the noble metal salt,

treating the dispersion layer with a nickel-plating solution containing nickel ions and a reducing agent at least until a continuous nickel layer is deposited thereon,

reinforcing the deposited nickel layer by electroplating,

deactivating the nickel layer by heating to 90 to and sintering the polytetrafluoroethylene layer at a temperature between about 380 and 400C.

2. A process according to claim 1 in which the surface of the metallic support is roughened to a depth of about 3 to 7 microns.

3. A process according to claim 1 in which the dispersion contains about 2 to 10 percent by weight of tin-Ilchloride as the activator.

4. A process according to claim 1 in which the dispersion contains about 3 t0 4 percent by weight of hydrazine hydrate as the activator.

5. A process according to claim 1 in which the dispersion contains less than about lpercent by weight of a wetting agent.

6. A process according to claim 8 in which the wetting agent is the ammonium salt of perfluorinated caprylicacid. I 

1. A PROCESS FOR THE MANUFACTURE OF A PHANOGRAPHIC PRINTING PLATE CAPABLE OF BEING PROCESSED INTO A PLANOGRAPHIC PRINTING FORM REQUIRING NO WETTING WHICH COMPRISES ROUGHENING THE SURFACE OF A METALLIC SUPPORT, COATING THE SURFACE WITH AN AT LAST ABOUT 30 PERCENT BY WEIGHT DISPERSION OF POLYERTAFLUOROETHYLENE CONTAINING A REDUCING ACTIVATOR CAPABLE OF REDUCING A NOBLE METAL IN A SOLUTION OF A SALT THEREOF, THE QUANITY OF DISPERSION APPLIED BEING SUCH THAT, AFTER BEING SINTERED, THE DISPERSION LAYER COMPLETELY COVERS THE ROUGHENED SURFACE, DRYING THE DISPERSION LAYER AT TEMPERATUREWS UP TO ABOUT 110*C., HEATING THE DRIED DISPERSION LAYER AT A TEMPERATURE BETWEEN ABOUT 180 AND 220*C., TREATING THE COOLED DISPERSION LAYER WITH A SENSITIZING SOLUTION CONTAINING A NOBLE METAL SALT, THUS FORMING NUCLEI OF THE NOBLE METAL SALT, TREATING THE DISPERSION LAYER WITH A NICKEL-PLATING SOLUTION CONTAINING NICKEL IONS AND A REDUCING AGENT AT LEAST UNTIL A CONTINOUS NICKEL LAYER IS DEPOSITED THEREON, REINFORCING THE DEPOSITED NICKEL LAYER BY ELECTROPLATING, DEACTIVATING THE NICKEL LAYER BY HEATING TO 90* TO 100*C., AND SINTERING THE POLYTETRAFLOUROETHYLENE LAYER AT A TEMPERATURE BETWEEN ABOUT 380* AD 400*C.
 2. A process according to claim 1 in which the surface of the metallic support is roughened to a depth of about 3 to 7 microns.
 3. A process according to claim 1 in which the dispersion contains about 2 to 10 percent by weight of tin-II-chloride as the activator.
 4. A process according to claim 1 in which the dispersion contains about 3 to 4 percent by weight of hydrazine hydrate as the activator.
 5. A process according to claim 1 in which the dispersion contains less than about 1 percent by weight of a wetting agent.
 6. A process according to claim 8 in which the wetting agent is the ammonium salt of perfluorinated caprylic acid. 